The phenomena of stabilized "cool flame" reactions wherein a mixture of hydrocarbon vapor and air is maintained at pressure and temperature conditions below that of an explosive reaction is well understood in the art. Particularly, for several years now, it has been known that certain measurable parameter values of a cool flame reaction involving the oxidation of a hydrocarbon mixture can be correlated to some characteristic of the hydrocarbon sample, specifically the octane rating for gasoline.
One such prior technique is disclosed in U.S. Pat. No. 3,738,810, which teaches that, when a gasoline is oxidized in a cool flame reaction, either the time elapsed between injection of the sample and the beginning of the reaction or the severity of the reaction (e.g., the peak height of the reaction) directly correlates with the octane number of that gasoline sample as determined by certified analysis by accepted ASTM methods on the combustible fuel research (CFR) engine. Such apparatus and method have achieved a degree of commercial success, due in part to the relatively low purchase and installation costs, ease of maintenance, and repeatability of measured values as compared to the current standard against which all octane rating numbers are based, i.e., the CFR engine.
Although the techniques disclosed in the aforementioned patent have been successfully demonstrated in a commercial device that works well in its intended application, it does suffer from certain drawbacks. For example, the device disclosed, being primarily analog, is subject to inaccuracies and slow response times as well as problems in interfacing with digital process control units commonly employed in today's chemical processing plants and refineries to provide highly accurate automatic regulation over the entire process. However, perhaps the most notable deficiency of this and other similar analyzers is their inability to perform on-line blending with process streams of widely varying composition without frequent recalibration with CFR engine rated standards. In the specific example of gasoline production, present analysis techniques allow on-line measurement of a particular, a priori defined, hydrocarbon blend. For example, during certain stages in the gasoline refining process, reformates are produced whose octane rating and consistency are known within well defined, narrow limits. Hence, although these prior art techniques make reference to the ability of performing "blending" operations, this form of blending referred to is limited in scope to constituents of small composition deviations and moreover occurs after considerable resources have been expended in the refining process. Accordingly, it represents a more expensive, less flexible operation.
Therefore, notwithstanding the usefulness of the prior art hydrocarbon analyzers operating with cool flame reactors, a need still exists for a highly accurate device capable of automatically blending mixtures containing widely varying compositions that is inexpensive and simple to operate and easily adapted to continuous on-line operation and computerized process management and control applications. This is especially true in a petrochemical refining process wherein large amounts of energy are required to produce a fuel of known composition and octane rating.